feat(pm): support packageManager self-pinning

[fireairforce]

Summary

Projects can now pin an exact Utoo package-manager version with "packageManager": "utoo@x.y.z", so contributors and CI use the same implementation instead of whichever global Utoo version happens to be installed.

• Honor exact packageManager pins for local dependency operations.
• Provision the matching supported platform package from the configured npm registry.
• Verify registry SRI/shasum metadata, cache the release in a platform-specific slot under a dedicated self-pin cache root, and revalidate the cached executable and reported version before handoff.
• Treat invalid cached releases as cache misses: never execute them, and replace only the affected platform slot after a newly downloaded archive passes registry integrity verification.
• Preserve command arguments, working directory, stdio, exit status, and signals during handoff.
• Keep scripts, ut x, query commands, and global installs on the current executable.
• Document the pinning flow and the UTOO_SELF_PIN=0 escape hatch.

Prior art: Nub provides the same project-level version selection through packageManager: "nub@x.y.z", provisioning and handing off to the exact pinned Nub release during install operations.

SchemaStore support is being added in SchemaStore/schemastore#6192. It updates the package.json schema pattern from:

-(npm|pnpm|yarn|bun|aube|nub)@\d+\.\d+\.\d+(-.+)?
+(npm|pnpm|yarn|bun|aube|nub|utoo)@\d+\.\d+\.\d+(-.+)?

The first release containing this feature should be utoo@1.1.8 or newer; older binaries do not understand the recursion/auto-update guard used by the handoff.

Test Plan

• cargo test -p utoo-pm — 369 unit tests and 28 CLI contract tests passed; 3 network tests ignored by the existing suite.
• Added regression coverage for platform-specific cache keys, malformed cache metadata, executable integrity mismatches, and self-pin cleanup serialization.
• Keep the self-pin cache physically isolated from ordinary registry packages while exposing logical _utoo-self-<platform>@<version> entries for exact utoo clean matching. Cleanup acquires the same platform/version lock as handoff and provisioning.
• On Windows, keep the slot locked through child process creation, then release it before waiting so nested utoo clean invocations cannot deadlock the handoff parent.
• cargo clippy --all-targets -- -D warnings --no-deps.
• cargo fmt --all -- --check.
• npx tombi format --check.
• typos on changed files.
• Manual corruption checks confirmed modified cached releases are never executed and fail closed if verified reprovisioning is unavailable.

[chatgpt-codex-connector]

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[elrrrrrrr]

LGTM